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Interference drag is greater when two surfaces meet at perpendicular angles, and can be minimised by the use of fairings. [6] [7] [5] Wave drag, also known as supersonic wave drag or compressibility drag, is a component of form drag caused by shock waves generated when an aircraft is moving at transonic and supersonic speeds. [1]: 25, 492, 573
Drag coefficients in fluids with Reynolds number approximately 10 4 [1] [2] Shapes are depicted with the same projected frontal area. In fluid dynamics, the drag coefficient (commonly denoted as: , or ) is a dimensionless quantity that is used to quantify the drag or resistance of an object in a fluid environment, such as air or water.
The equation is precise – it simply provides the definition of (drag coefficient), which varies with the Reynolds number and is found by experiment. Of particular importance is the u 2 {\displaystyle u^{2}} dependence on flow velocity, meaning that fluid drag increases with the square of flow velocity.
Parasitic drag, or profile drag, is the sum of viscous pressure drag (form drag) and drag due to surface roughness (skin friction drag). Additionally, the presence of multiple bodies in relative proximity may incur so called interference drag , which is sometimes described as a component of parasitic drag.
A form factor (i) greater than 1 indicates the particular projectile exhibits more drag than the applied reference projectile shape. [66] In general the G1 model yields comparatively high BC values and is often used by the sporting ammunition industry.
Skin friction drag is generally expressed in terms of the Reynolds number, which is the ratio between inertial force and viscous force. Total drag can be decomposed into a skin friction drag component and a pressure drag component, where pressure drag includes all other sources of drag including lift-induced drag. [1]
This decomposition separates the effect of the lift coefficient in the equation, obtaining two terms C D0 and C Di. C D0 is known as the parasitic drag coefficient and it is the base drag coefficient at zero lift. C Di is known as the induced drag coefficient and it is produced by the body lift.
The drag curve or drag polar is the relationship between the drag on an aircraft and other variables, such as lift, the coefficient of lift, angle-of-attack or speed. It may be described by an equation or displayed as a graph (sometimes called a "polar plot"). [1] Drag may be expressed as actual drag or the coefficient of drag.